Some people here have had a lot of luck housetraining their dogs and some probably just have a knack at training dogs in general or are very, very knowledgable at training. Most small breeds are harder to train than large breeds and yorkies are not easy to housebreak as a rule. Of course it can be done but it takes a lot of time and effort and it is good that you are making an informed decision. I had our first dog (a mix, 20 pounds) completely trained by 12 weeks. Our first yorkie took until she was 6 months to start to get it and wasn't 100% until she was a year. I grew up around dogs and for me, the yorkies have been, by far, the biggest challenge. I personally love yorkies despite their difficulty to house train but if this isn't the case for you, it is good that you know now. IMO yorkies are the very best breed in the world but if you are concerned with a housebreaking challenge, they aren't for you. Good luck with your decision.
__________________
"If you have men who will exclude any of God’s creatures from the shelter of compassion and pity, you will have men who will deal likewise with their fellow men." — St. Francis of Assisi, 1181-1226